Augmented reality systems and methods with variable focus lens elements

ABSTRACT

An augmented reality display system includes a pair of variable focus lens elements that sandwich a waveguide stack. One of the lens elements is positioned between the waveguide stack and a user&#39;s eye to correct for refractive errors in the focusing of light projected from the waveguide stack to that eye. The lens elements may also be configured to provide appropriate optical power to place displayed virtual content on a desired depth plane. The other lens element is between the ambient environment and the waveguide stack, and is configured to provide optical power to compensate for aberrations in the transmission of ambient light through the waveguide stack and the lens element closest to the eye. In addition, an eye-tracking system monitors the vergence of the user&#39;s eyes and automatically and continuously adjusts the optical powers of the pair of lens elements based on the determined vergence of those eyes.

PRIORITY CLAIM

This application is a continuation of U.S. application Ser. No.16/664,191 filed on Oct. 25, 2019, entitled “AUGMENTED REALITY SYSTEMSAND METHODS WITH VARIABLE FOCUS LENS ELEMENTS”, which is a continuationof U.S. application Ser. No. 15/481,255 filed on Apr. 6, 2017, entitled“AUGMENTED REALITY SYSTEMS AND METHODS WITH VARIABLE FOCUS LENSELEMENTS” (now U.S. Ser. No. 10/459,231), which claims the prioritybenefit of U.S. Provisional Patent Application No. 62/320,375 filed onApr. 8, 2016, entitled “AUGMENTED REALITY SYSTEMS AND METHODS WITHVARIABLE FOCUS LENS ELEMENTS,” which is incorporated by reference hereinin its entirety.

INCORPORATION BY REFERENCE

This application also incorporates by reference the entirety of each ofthe following patent applications: U.S. application Ser. No. 14/555,585filed on Nov. 27, 2014; U.S. application Ser. No. 14/690,401 filed onApr. 18, 2015; U.S. application Ser. No. 14/212,961 filed on Mar. 14,2014; U.S. application Ser. No. 14/331,218 filed on Jul. 14, 2014; andU.S. application Ser. No. 15/072,290 filed on Mar. 16, 2016.

BACKGROUND Field

The present disclosure relates to optical devices, including augmentedreality imaging and visualization systems.

Description of the Related Art

Modern computing and display technologies have facilitated thedevelopment of systems for so called “virtual reality” or “augmentedreality” experiences, in which digitally reproduced images or portionsthereof are presented to a user in a manner wherein they seem to be, ormay be perceived as, real. A virtual reality, or “VR”, scenariotypically involves the presentation of digital or virtual imageinformation without transparency to other actual real-world visualinput; an augmented reality, or “AR”, scenario typically involvespresentation of digital or virtual image information as an augmentationto visualization of the actual world around the user. A mixed reality,or “MR”, scenario is a type of AR scenario and typically involvesvirtual objects that are integrated into, and responsive to, the naturalworld. For example, an MR scenario may include AR image content thatappears to be blocked by or is otherwise perceived to interact withobjects in the real world.

Referring to FIG. 1, an augmented reality scene 10 is depicted. The userof an AR technology sees a real-world park-like setting 20 featuringpeople, trees, buildings in the background, and a concrete platform 30.The user also perceives that he/she “sees” “virtual content” such as arobot statue 40 standing upon the real-world platform 30, and a flyingcartoon-like avatar character 50 which seems to be a personification ofa bumble bee. These elements 50, 40 are “virtual” in that they do notexist in the real world. Because the human visual perception system iscomplex, it is challenging to produce AR technology that facilitates acomfortable, natural-feeling, rich presentation of virtual imageelements amongst other virtual or real-world imagery elements.

Systems and methods disclosed herein address various challenges relatedto AR and VR technology.

SUMMARY

In some embodiments, a display system is provided. The display systemcomprises a head-mountable display configured to project light to aviewer to display image information on one or more depth planes. Thedisplay comprises one or more waveguides configured to project the lightto the viewer. The one or more waveguides are further configured totransmit light from objects in a surrounding environment to the viewer.The display also comprises a first variable focus lens element betweenthe one or more waveguides and a first eye of the viewer; and a secondvariable focus lens element between the one or more waveguides and thesurrounding environment. An eye tracking system is configured todetermine vergence of the viewer's eyes. The display system isconfigured to correct a refractive error of the user's eyes by adjustingan optical power of the first and second variable focus lens elementsbased on the determined vergence of the viewer's eyes.

In some other embodiments, a method for displaying image information ona head-mountable display is provided. The method comprises providing thedisplay mounted on a head of a viewer, with the display configured todisplay image information on one or more depth planes. The displaycomprises one or more waveguides configured to project light to theviewer to display the image information. The one or more waveguides arefurther configured to transmit light from objects in a surroundingenvironment to the viewer. The method further comprises determining avergence point of eyes of the viewer and correcting a refractive errorof an eye of the viewer. The refractive error may be corrected byvarying optical power of a first variable focus lens element disposedbetween the one or more waveguides and an eye of the viewer based on thedetermined vergence point; and varying optical power of a secondvariable focus lens element disposed between the one or more waveguidesand an environment surrounding the viewer based on the determinedvergence point.

Example 1: A display system comprising:

a head-mountable display configured to project light to a viewer todisplay image information on one or more depth planes, the displaycomprising:

one or more waveguides configured to project the light to the viewer,wherein the one or more waveguides are further configured to transmitlight from objects in a surrounding environment to the viewer;

a first variable focus lens element between the one or more waveguidesand a first eye of the viewer; and

a second variable focus lens element between the one or more waveguidesand the surrounding environment; and

an eye tracking system configured to determine vergence of the viewer'seyes, wherein the display system is configured to correct a refractiveerror of the user's eyes by adjusting an optical power of the first andsecond variable focus lens elements based on the determined vergence ofthe viewer's eyes.

Example 2: The display system of Example 1, wherein the display systemis configured to modify the optical power of the first and secondvariable focus lens elements depending on a depth plane for displayingthe image information.

Example 3: The display system of any of Examples 1-2, wherein thedisplay system is configured to adjust an optical power of the secondvariable focus lens element in response to an optical power of the firstvariable focus lens element.

Example 4: The display system of any of Examples 1-3, wherein the one ormore waveguides are configured to project divergent light to the viewerto display the image information.

Example 5: The display system of any of Example 1-4, wherein each of theone or more waveguides has a fixed optical power.

Example 6: The display system of any of Examples 1-5, further comprisinga third variable focus element between the one or more waveguides and asecond eye of the viewer.

Example 7: The display system of Example 6, further comprising a fourthvariable focus element between the one or more waveguides and thesurrounding environment.

Example 8: The display system of any of Examples 6-7, wherein the systemis configured to adjust an optical power of the third variable focuslens element to vary the wavefront of the projected light based on thedetermined vergence.

Example 9: The display system of any of Examples 6-8, wherein the systemis configured to adjust an optical power of the fourth variable focuslens element to vary the wavefront of incoming light from the object inthe surrounding environment based on the determined vergence.

Example 10: The display system of any of Examples 1-9, wherein eyetracking system comprises one or more cameras.

Example 11: The display system of any of Examples 1-10, wherein anoptical power of the first and/or second variable focus lens element isadjusted in accordance with a prescription for correcting the viewer'svision at two or more distances.

Example 12: The display system of any of Examples 1-11, wherein thesystem has three or more preset prescription optical powers for each ofthe first and second variable focus lens elements.

Example 13: The display system of any of Examples 1-12, wherein a numberof available prescription optical powers is equal to at least a totalnumber of depth planes for the display.

Example 14: The display system of any of Examples 1-13, wherein thefirst and/or second variable focus lens elements comprises a layer ofliquid crystal sandwiched between two substrates.

Example 15: The display system of the Example 14, wherein the firstand/or second variable focus lens elements comprise electrodes foraltering a refractive index of the liquid crystal layer upon applicationof a voltage.

Example 16: The display system of Examples 14-15, wherein the substratescomprise glass.

Example 17: The display system of any of Examples 1-16, furthercomprising an electronic hardware control system configured to vary therefractive index of the first and/or second variable focus lens elementby application of an electrical current or voltage.

Example 18: The display system of Example 17, wherein the eye trackingsystem forms a feedback loop to the electronic hardware control systemto vary the refractive index of the first and/or second variable focuslens element in accordance with the determined vergence of the viewer'seyes.

Example 19: A method for displaying image information on ahead-mountable display, the method comprising:

providing the display mounted on a head of a viewer, the displayconfigured to display image information on one or more depth planes andcomprising:

one or more waveguides configured to project light to the viewer todisplay the image information, wherein the one or more waveguides arefurther configured to transmit light from objects in a surroundingenvironment to the viewer;

determining a vergence point of eyes of the viewer; and

correcting a refractive error of an eye of the viewer by:

-   -   varying optical power of a first variable focus lens element        disposed between the one or more waveguides and an eye of the        viewer based on the determined vergence point; and varying        optical power of a second variable focus lens element disposed        between the one or more waveguides and an environment        surrounding the viewer based on the determined vergence point.

Example 20: The method of Example 19, further comprising:

a third variable focus lens element and a fourth variable focus lenselement, wherein the third variable focus lens element is between theone or more waveguides and an other eye of the viewer, and wherein thefourth variable focus lens element is directly forward of the thirdvariable focus lens and between the one or more waveguides and thesurrounding environment; and correcting a refractive error of the othereye by varying an optical power of the third and fourth variable focuslens elements based on the determined vergence point.

Example 21: The method of Example 20, wherein determining the vergencepoint comprises tracking a vergence of the eye and the other eye of theviewer using one or more cameras.

Example 22: The method of any of Examples 19-21, wherein the opticalpower of the first variable focus lens element is varied simultaneouslywith the optical power of the second variable focus lens element.

Example 23: The method of any of Examples 19-22, wherein the one or morewaveguides each comprises diffractive optical elements configured tooutput divergent light from the waveguides.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a user's view of augmented reality (AR) through an ARdevice.

FIG. 2 illustrates an example of wearable display system.

FIG. 3 illustrates a conventional display system for simulatingthree-dimensional imagery for a user.

FIG. 4 illustrates aspects of an approach for simulatingthree-dimensional imagery using multiple depth planes.

FIGS. 5A-5C illustrate relationships between radius of curvature andfocal radius.

FIG. 6 illustrates an example of a waveguide stack for outputting imageinformation to a user.

FIG. 7 illustrates an example of exit beams outputted by a waveguide.

FIG. 8 illustrates an example of a stacked waveguide assembly in whicheach depth plane includes images formed using multiple differentcomponent colors.

FIG. 9A illustrates a cross-sectional side view of an example of a setof stacked waveguides that each includes an incoupling optical element.

FIG. 9B illustrates a perspective view of an example of the plurality ofstacked waveguides of FIG. 9A.

FIG. 9C illustrates a top-down plan view of an example of the pluralityof stacked waveguides of FIGS. 9A and 9B.

FIGS. 10A and 10B are schematic illustrations of examples of displayshaving variable focus lens elements and one or more waveguides. FIG. 10Ashows a waveguide stack with a single waveguide, and FIG. 10B shows awaveguide stack with a plurality of waveguides.

FIG. 11 shows a schematic view of various components of an augmentedreality system comprising an eye tracking system.

FIG. 12 depicts an example of a method for varying optical power ofvariable focus lens elements based on the vergence of a user's eyes.

The drawings are provided to illustrate example embodiments and are notintended to limit the scope of the disclosure.

DETAILED DESCRIPTION

As disclosed herein, augmented reality (AR) systems may display virtualcontent to a viewer while still allowing the viewer to see the worldaround them. Preferably, this content is displayed on a head-mountabledisplay, e.g., as part of eyewear, that projects image information tothe viewer's eyes, while also transmitting light from the surroundingenvironment to those eyes, to allow a view of that surroundingenvironment.

Many viewers, however, have eyes with refractive errors that preventlight from correctly focusing on their eyes' retinas. Examples ofrefractive errors include myopia, hyperopia, presbyopia, andastigmatism. These viewers may require lens elements with a particularprescription optical power to clearly view the image informationprojected by the display. In some embodiments, such lens elements may bepositioned between a waveguide for projecting the image information andthe viewer's eyes. Undesirably, these lens elements and possibly otheroptically transmissive parts of the display, such as the waveguides, maycause aberrations in the viewer's view of the surrounding environment.In addition, many lens elements have a fixed optical power that may notaddress all of the refractive errors experienced by a viewer.

In some embodiments, a display system includes first and second variablefocus lens elements that sandwich (are positioned on either side of) awaveguide or plurality of waveguides. The first lens element may bebetween the one or more waveguides and an eye of the viewer, and may beconfigured to correct for refractive errors in the focusing of lightprojected from the one or more waveguides to that eye. In addition, insome embodiments, the first lens elements may be configured to providean appropriate amount of optical power to place displayed virtualcontent on a desired depth plane. The second lens element may be betweenthe surrounding environment and the one or more waveguides, and may beconfigured to provide optical power to compensate for aberrations in thetransmission of light from the surrounding environment through thewaveguides and first lens element. In some embodiments, refractiveerrors in the viewer's other eye may be separately corrected. Forexample, a third variable focus lens elements between the other eye andthe waveguides, and fourth variable focus lens elements between thewaveguides and the surrounding environment may be used to correct forrefractive errors in this other eye. The focal length/optical power ofthe variable focus elements may be varied such that the real worldand/or the virtual content are focused on the retina of the user's eye,thereby allowing the user to view both the real and virtual objects withhigh optical image quality.

In some embodiments, the display is part of a display system thatincludes an eye tracking system configured to determine the vergence ofthe viewer's eye. The eye tracking system may be, e.g., one or morecameras that determine the vergence point of the eyes and, as a result,may be utilized to determine the distance at which the eyes are focused,to derive the appropriate correction for the eyes for that distance. Itwill be appreciated that different corrections maybe required fordifferent vergence points, e.g., different corrections may be requiredfor the viewer's eyes to properly focus on near, far, or intermediateobjects (whether real or virtual objects). In some embodiments, theability of the variable focus lens elements to provide variable opticalpower may allow gradations of correction not readily available for,e.g., prescription eye glasses or contact lenses. For example, two ormore, three or more, four or more, or five or more unique corrections(for each eye, in some embodiments) may be available.

Instead of wearing fixed prescription optics, the variable focus lenselements may be configured to provide the desired correction to theuser. For example, the augmented reality display system may beconfigured to provide different optical power for virtual objectsprojected from different depth planes and/or for real-world objects atdifferent distances. For example, for users requiring near visioncorrection the variable focus lens elements may be configured to providea near vision optical power when the user is viewing virtual objects orreal-world objects located at distances corresponding to near visionzone. As another example, for users requiring intermediate distancevision correction, the variable focus lens elements may be configured toprovide an intermediate distance vision optical power when the user isviewing virtual objects or real-world objects located at distancescorresponding to intermediate distance vision zone. As yet anotherexample, for users requiring far vision correction, the variable focuslens elements may be configured to provide a far vision optical powerwhen the user is viewing virtual objects or real-world objects locatedat distances corresponding to a far vision zone. In some embodiments, auser's prescription for near vision correction, intermediate distancevision correction and far vision correction may be accessed by thedisplay system and the system may vary the optical power of the variablefocus lens elements in accordance with the user's prescription when theuser is viewing virtual objects or real-world objects located atdistances corresponding to the near vision zone, intermediate distancevision zone, and far vision zone.

Advantageously, the first and/or second lens elements may allow the samehead-mountable display to be used by a variety of users, withoutphysically changing out corrective lens elements. Rather, the displaysadapt to the user. In addition, the variable focus lens elements may beconfigured to provide the appropriate optical power to place imageinformation projected from the one or more waveguides on a desired depthplane. For example, the variable focus lens elements may be configuredto vary the divergence of light projected from the one or morewaveguides to the viewer. The adaptability provided by the variablefocus lens elements may provide advantages for simplifying themanufacture and design of the display, since the same display may beprovided to and used by different users and fewer optical structures maybe required to display image information on a range of depth planes.Moreover, the ability to offer a wide range of corrections in real timemay allow for a larger number of gradations for correction than readilyavailable with conventional corrective glasses. This may improve thesharpness and/or acuity of the viewer's view of the world and displayedimage information, and may also facilitate long-term viewer comfort. Inaddition, the variable focus lens elements may be configured withdifferent prescriptions by simply changing preset corrections programmedinto the display system, thereby allowing the display to readily adaptto new user prescriptions as, e.g., the user ages and the condition ofone or both eyes changes.

Reference will now be made to the figures, in which like referencenumerals refer to like parts throughout.

FIG. 2 illustrates an example of wearable display system 60. The displaysystem 60 includes a display 70, and various mechanical and electronicmodules and systems to support the functioning of that display 70. Thedisplay 70 may be coupled to a frame 80, which is wearable by a displaysystem user or viewer 90 and which is configured to position the display70 in front of the eyes of the user 90. The display 70 may be consideredeyewear in some embodiments. In some embodiments, a speaker 100 iscoupled to the frame 80 and configured to be positioned adjacent the earcanal of the user 90 (in some embodiments, another speaker, not shown,may optionally be positioned adjacent the other ear canal of the user toprovide stereo/shapeable sound control). The display system may alsoinclude one or more microphones 110 or other devices to detect sound. Insome embodiments, the microphone is configured to allow the user toprovide inputs or commands to the system 60 (e.g., the selection ofvoice menu commands, natural language questions, etc.), and/or may allowaudio communication with other persons (e.g., with other users ofsimilar display systems. The microphone may further be configured as aperipheral sensor to collect audio data (e.g., sounds from the userand/or environment). In some embodiments, the display system may alsoinclude a peripheral sensor 120 a, which may be separate from the frame80 and attached to the body of the user 90 (e.g., on the head, torso, anextremity, etc. of the user 90). The peripheral sensor 120 a may beconfigured to acquire data characterizing a physiological state of theuser 90 in some embodiments. For example, the sensor 120 a may be anelectrode.

With continued reference to FIG. 2, the display 70 is operativelycoupled by communications link 130, such as by a wired lead or wirelessconnectivity, to a local data processing module 140 which may be mountedin a variety of configurations, such as fixedly attached to the frame80, fixedly attached to a helmet or hat worn by the user, embedded inheadphones, or otherwise removably attached to the user 90 (e.g., in abackpack-style configuration, in a belt-coupling style configuration).Similarly, the sensor 120 a may be operatively coupled by communicationslink 120 b, e.g., a wired lead or wireless connectivity, to the localprocessor and data module 140. The local processing and data module 140may comprise a hardware processor, as well as digital memory, such asnon-volatile memory (e.g., flash memory or hard disk drives), both ofwhich may be utilized to assist in the processing, caching, and storageof data. The data include data a) captured from sensors (which may be,e.g., operatively coupled to the frame 80 or otherwise attached to theuser 90), such as image capture devices (such as cameras), microphones,inertial measurement units, accelerometers, compasses, GPS units, radiodevices, gyros, and/or other sensors disclosed herein; and/or b)acquired and/or processed using remote processing module 150 and/orremote data repository 160 (including data relating to virtual content),possibly for passage to the display 70 after such processing orretrieval. The local processing and data module 140 may be operativelycoupled by communication links 170, 180, such as via a wired or wirelesscommunication links, to the remote processing module 150 and remote datarepository 160 such that these remote modules 150, 160 are operativelycoupled to each other and available as resources to the local processingand data module 140. In some embodiments, the local processing and datamodule 140 may include one or more of the image capture devices,microphones, inertial measurement units, accelerometers, compasses, GPSunits, radio devices, and/or gyros. In some other embodiments, one ormore of these sensors may be attached to the frame 80, or may bestandalone structures that communicate with the local processing anddata module 140 by wired or wireless communication pathways.

With continued reference to FIG. 2, in some embodiments, the remoteprocessing module 150 may comprise one or more processors configured toanalyze and process data and/or image information. In some embodiments,the remote data repository 160 may comprise a digital data storagefacility, which may be available through the internet or othernetworking configuration in a “cloud” resource configuration. In someembodiments, the remote data repository 160 may include one or moreremote servers, which provide information, e.g., information forgenerating augmented reality content, to the local processing and datamodule 140 and/or the remote processing module 150. In some embodiments,all data is stored and all computations are performed in the localprocessing and data module, allowing fully autonomous use from a remotemodule.

With reference now to FIG. 3, the perception of an image as being“three-dimensional” or “3-D” may be achieved by providing slightlydifferent presentations of the image to each eye of the viewer. FIG. 3illustrates a conventional display system for simulatingthree-dimensional imagery for a user. Two distinct images 190, 200—onefor each eye 210, 220—are outputted to the user. The images 190, 200 arespaced from the eyes 210, 220 by a distance 230 along an optical orz-axis that is parallel to the line of sight of the viewer. The images190, 200 are flat and the eyes 210, 220 may focus on the images byassuming a single accommodated state. Such 3-D display systems rely onthe human visual system to combine the images 190, 200 to provide aperception of depth and/or scale for the combined image.

It will be appreciated, however, that the human visual system is morecomplicated and providing a realistic perception of depth is morechallenging. For example, many viewers of conventional “3-D” displaysystems find such systems to be uncomfortable or may not perceive asense of depth at all. Without being limited by theory, it is believedthat viewers of an object may perceive the object as being“three-dimensional” due to a combination of vergence and accommodation.Vergence movements (i.e., rotation of the eyes so that the pupils movetoward or away from each other to converge the lines of sight of theeyes to fixate upon an object) of the two eyes relative to each otherare closely associated with focusing (or “accommodation”) of the lensesand pupils of the eyes. Under normal conditions, changing the focus ofthe lenses of the eyes, or accommodating the eyes, to change focus fromone object to another object at a different distance will automaticallycause a matching change in vergence to the same distance, under arelationship known as the “accommodation-vergence reflex,” as well aspupil dilation or constriction. Likewise, a change in vergence willtrigger a matching change in accommodation of lens shape and pupil size,under normal conditions. As noted herein, many stereoscopic or “3-D”display systems display a scene using slightly different presentations(and, so, slightly different images) to each eye such that athree-dimensional perspective is perceived by the human visual system.Such systems are uncomfortable for many viewers, however, since they,among other things, simply provide different presentations of a scene,but with the eyes viewing all the image information at a singleaccommodated state, and work against the “accommodation-vergencereflex.” Display systems that provide a better match betweenaccommodation and vergence may form more realistic and comfortablesimulations of three-dimensional imagery.

FIG. 4 illustrates aspects of an approach for simulatingthree-dimensional imagery using multiple depth planes. With reference toFIG. 4, objects at various distances from eyes 210, 220 on the z-axisare accommodated by the eyes 210, 220 so that those objects are infocus. The eyes 210, 220 assume particular accommodated states to bringinto focus objects at different distances along the z-axis.Consequently, a particular accommodated state may be said to beassociated with a particular one of depth planes 240, with has anassociated focal distance, such that objects or parts of objects in aparticular depth plane are in focus when the eye is in the accommodatedstate for that depth plane. In some embodiments, three-dimensionalimagery may be simulated by providing different presentations of animage for each of the eyes 210, 220, and also by providing differentpresentations of the image corresponding to each of the depth planes.While shown as being separate for clarity of illustration, it will beappreciated that the fields of view of the eyes 210, 220 may overlap,for example, as distance along the z-axis increases. In addition, whileshown as flat for ease of illustration, it will be appreciated that thecontours of a depth plane may be curved in physical space, such that allfeatures in a depth plane are in focus with the eye in a particularaccommodated state.

The distance between an object and the eye 210 or 220 may also changethe amount of divergence of light from that object, as viewed by thateye. FIGS. 5A-5C illustrate relationships between distance and thedivergence of light rays. The distance between the object and the eye210 is represented by, in order of decreasing distance, R1, R2, and R3.As shown in FIGS. 5A-5C, the light rays become more divergent asdistance to the object decreases. As distance increases, the light raysbecome more collimated. Stated another way, it may be said that thelight field produced by a point (the object or a part of the object) hasa spherical wavefront curvature, which is a function of how far away thepoint is from the eye of the user. The curvature increases withdecreasing distance between the object and the eye 210. Consequently, atdifferent depth planes, the degree of divergence of light rays is alsodifferent, with the degree of divergence increasing with decreasingdistance between depth planes and the viewer's eye 210. While only asingle eye 210 is illustrated for clarity of illustration in FIGS. 5A-5Cand other figures herein, it will be appreciated that the discussionsregarding eye 210 may be applied to both eyes 210 and 220 of a viewer.

Without being limited by theory, it is believed that the human eyetypically can interpret a finite number of depth planes to provide depthperception. Consequently, a highly believable simulation of perceiveddepth may be achieved by providing, to the eye, different presentationsof an image corresponding to each of these limited number of depthplanes. The different presentations may be separately focused by theviewer's eyes, thereby helping to provide the user with depth cues basedon the accommodation of the eye required to bring into focus differentimage features for the scene located on different depth plane and/orbased on observing different image features on different depth planesbeing out of focus.

FIG. 6 illustrates an example of a waveguide stack for outputting imageinformation to a user. A display system 250 includes a stack ofwaveguides, or stacked waveguide assembly, 260 that may be utilized toprovide three-dimensional perception to the eye/brain using a pluralityof waveguides 270, 280, 290, 300, 310. In some embodiments, the displaysystem 250 is the system 60 of FIG. 2, with FIG. 6 schematically showingsome parts of that system 60 in greater detail. For example, thewaveguide assembly 260 may be part of the display 70 of FIG. 2. It willbe appreciated that the display system 250 may be considered a lightfield display in some embodiments. In addition, the waveguide assembly260 may also be referred to as an eyepiece.

With continued reference to FIG. 6, the waveguide assembly 260 may alsoinclude a plurality of features 320, 330, 340, 350 between thewaveguides. In some embodiments, the features 320, 330, 340, 350 may beone or more lenses. The waveguides 270, 280, 290, 300, 310 and/or theplurality of lenses 320, 330, 340, 350 may be configured to send imageinformation to the eye with various levels of wavefront curvature orlight ray divergence. Each waveguide level may be associated with aparticular depth plane and may be configured to output image informationcorresponding to that depth plane. Image injection devices 360, 370,380, 390, 400 may function as a source of light for the waveguides andmay be utilized to inject image information into the waveguides 270,280, 290, 300, 310, each of which may be configured, as describedherein, to distribute incoming light across each respective waveguide,for output toward the eye 210. Light exits an output surface 410, 420,430, 440, 450 of the image injection devices 360, 370, 380, 390, 400 andis injected into a corresponding input surface 460, 470, 480, 490, 500of the waveguides 270, 280, 290, 300, 310. In some embodiments, the eachof the input surfaces 460, 470, 480, 490, 500 may be an edge of acorresponding waveguide, or may be part of a major surface of thecorresponding waveguide (that is, one of the waveguide surfaces directlyfacing the world 510 or the viewer's eye 210). In some embodiments, asingle beam of light (e.g. a collimated beam) may be injected into eachwaveguide to output an entire field of cloned collimated beams that aredirected toward the eye 210 at particular angles (and amounts ofdivergence) corresponding to the depth plane associated with aparticular waveguide. In some embodiments, a single one of the imageinjection devices 360, 370, 380, 390, 400 may be associated with andinject light into a plurality (e.g., three) of the waveguides 270, 280,290, 300, 310.

In some embodiments, the image injection devices 360, 370, 380, 390, 400are discrete displays that each produce image information for injectioninto a corresponding waveguide 270, 280, 290, 300, 310, respectively. Insome other embodiments, the image injection devices 360, 370, 380, 390,400 are the output ends of a single multiplexed display which may, e.g.,pipe image information via one or more optical conduits (such as fiberoptic cables) to each of the image injection devices 360, 370, 380, 390,400. It will be appreciated that the image information provided by theimage injection devices 360, 370, 380, 390, 400 may include light ofdifferent wavelengths, or colors (e.g., different component colors, asdiscussed herein).

In some embodiments, the light injected into the waveguides 270, 280,290, 300, 310 is provided by a light projector system 520, whichcomprises a light module 540, which may include a light emitter, such asa light emitting diode (LED). The light from the light module 540 may bedirected to and modified by a light modulator 530, e.g., a spatial lightmodulator, via a beam splitter 550. The light modulator 530 may beconfigured to change the perceived intensity of the light injected intothe waveguides 270, 280, 290, 300, 310. Examples of spatial lightmodulators include liquid crystal displays (LCD) including a liquidcrystal on silicon (LCOS) displays. It will be appreciated that theimage injection devices 360, 370, 380, 390, 400 are illustratedschematically and, in some embodiments, these image injection devicesmay represent different light paths and locations in a common projectionsystem configured to output light into associated ones of the waveguides270, 280, 290, 300, 310.

In some embodiments, the display system 250 may be a scanning fiberdisplay comprising one or more scanning fibers configured to projectlight in various patterns (e.g., raster scan, spiral scan, Lissajouspatterns, etc.) into one or more waveguides 270, 280, 290, 300, 310 andultimately to the eye 210 of the viewer. In some embodiments, theillustrated image injection devices 360, 370, 380, 390, 400 mayschematically represent a single scanning fiber or a bundle of scanningfibers configured to inject light into one or a plurality of thewaveguides 270, 280, 290, 300, 310. In some other embodiments, theillustrated image injection devices 360, 370, 380, 390, 400 mayschematically represent a plurality of scanning fibers or a plurality ofbundles of scanning fibers, each of which are configured to inject lightinto an associated one of the waveguides 270, 280, 290, 300, 310. Itwill be appreciated that one or more optical fibers may be configured totransmit light from the light module 540 to the one or more waveguides270, 280, 290, 300, 310. It will be appreciated that one or moreintervening optical structures may be provided between the scanningfiber, or fibers, and the one or more waveguides 270, 280, 290, 300, 310to, e.g., redirect light exiting the scanning fiber into the one or morewaveguides 270, 280, 290, 300, 310.

A controller 560 controls the operation of one or more of the stackedwaveguide assembly 260, including operation of the image injectiondevices 360, 370, 380, 390, 400, the light source 540, and the lightmodulator 530. In some embodiments, the controller 560 is part of thelocal data processing module 140. The controller 560 includesprogramming (e.g., instructions in a non-transitory medium) thatregulates the timing and provision of image information to thewaveguides 270, 280, 290, 300, 310 according to, e.g., any of thevarious schemes disclosed herein. In some embodiments, the controllermay be a single integral device, or a distributed system connected bywired or wireless communication channels. The controller 560 may be partof the processing modules 140 or 150 (FIG. 2) in some embodiments.

With continued reference to FIG. 6, the waveguides 270, 280, 290, 300,310 may be configured to propagate light within each respectivewaveguide by total internal reflection (TIR). The waveguides 270, 280,290, 300, 310 may each be planar or have another shape (e.g., curved),with major top and bottom surfaces and edges extending between thosemajor top and bottom surfaces. In the illustrated configuration, thewaveguides 270, 280, 290, 300, 310 may each include out-coupling opticalelements 570, 580, 590, 600, 610 that are configured to extract lightout of a waveguide by redirecting the light, propagating within eachrespective waveguide, out of the waveguide to output image informationto the eye 210. Extracted light may also be referred to as out-coupledlight and the out-coupling optical elements light may also be referredto light extracting optical elements. An extracted beam of light may beoutputted by the waveguide at locations at which the light propagatingin the waveguide strikes a light extracting optical element. Theout-coupling optical elements 570, 580, 590, 600, 610 may, for example,be gratings, including diffractive optical features, as discussedfurther herein. While illustrated disposed at the bottom major surfacesof the waveguides 270, 280, 290, 300, 310, for ease of description anddrawing clarity, in some embodiments, the out-coupling optical elements570, 580, 590, 600, 610 may be disposed at the top and/or bottom majorsurfaces, and/or may be disposed directly in the volume of thewaveguides 270, 280, 290, 300, 310, as discussed further herein. In someembodiments, the out-coupling optical elements 570, 580, 590, 600, 610may be formed in a layer of material that is attached to a transparentsubstrate to form the waveguides 270, 280, 290, 300, 310. In some otherembodiments, the waveguides 270, 280, 290, 300, 310 may be a monolithicpiece of material and the out-coupling optical elements 570, 580, 590,600, 610 may be formed on a surface and/or in the interior of that pieceof material.

With continued reference to FIG. 6, as discussed herein, each waveguide270, 280, 290, 300, 310 is configured to output light to form an imagecorresponding to a particular depth plane. For example, the waveguide270 nearest the eye may be configured to deliver collimated light (whichwas injected into such waveguide 270), to the eye 210. The collimatedlight may be representative of the optical infinity focal plane. Thenext waveguide up 280 may be configured to send out collimated lightwhich passes through the first lens 350 (e.g., a negative lens) beforeit can reach the eye 210; such first lens 350 may be configured tocreate a slight convex wavefront curvature so that the eye/braininterprets light coming from that next waveguide up 280 as coming from afirst focal plane closer inward toward the eye 210 from opticalinfinity. Similarly, the third up waveguide 290 passes its output lightthrough both the first 350 and second 340 lenses before reaching the eye210; the combined optical power of the first 350 and second 340 lensesmay be configured to create another incremental amount of wavefrontcurvature so that the eye/brain interprets light coming from the thirdwaveguide 290 as coming from a second focal plane that is even closerinward toward the person from optical infinity than was light from thenext waveguide up 280.

The other waveguide layers 300, 310 and lenses 330, 320 are similarlyconfigured, with the highest waveguide 310 in the stack sending itsoutput through all of the lenses between it and the eye for an aggregatefocal power representative of the closest focal plane to the person. Tocompensate for the stack of lenses 320, 330, 340, 350 whenviewing/interpreting light coming from the world 510 on the other sideof the stacked waveguide assembly 260, a compensating lens layer 620 maybe disposed at the top of the stack to compensate for the aggregatepower of the lens stack 320, 330, 340, 350 below. Such a configurationprovides as many perceived focal planes as there are availablewaveguide/lens pairings. Both the out-coupling optical elements of thewaveguides and the focusing aspects of the lenses may be static (i.e.,not dynamic or electro-active). In some alternative embodiments, eitheror both may be dynamic using electro-active features.

In some embodiments, two or more of the waveguides 270, 280, 290, 300,310 may have the same associated depth plane. For example, multiplewaveguides 270, 280, 290, 300, 310 may be configured to output imagesset to the same depth plane, or multiple subsets of the waveguides 270,280, 290, 300, 310 may be configured to output images set to the sameplurality of depth planes, with one set for each depth plane. This canprovide advantages for forming a tiled image to provide an expandedfield of view at those depth planes.

With continued reference to FIG. 6, the out-coupling optical elements570, 580, 590, 600, 610 may be configured to both redirect light out oftheir respective waveguides and to output this light with theappropriate amount of divergence or collimation for a particular depthplane associated with the waveguide. As a result, waveguides havingdifferent associated depth planes may have different configurations ofout-coupling optical elements 570, 580, 590, 600, 610, which outputlight with a different amount of divergence depending on the associateddepth plane. In some embodiments, the light extracting optical elements570, 580, 590, 600, 610 may be volumetric or surface features, which maybe configured to output light at specific angles. For example, the lightextracting optical elements 570, 580, 590, 600, 610 may be volumeholograms, surface holograms, and/or diffraction gratings. In someembodiments, the features 320, 330, 340, 350 may not be lenses; rather,they may simply be spacers (e.g., cladding layers and/or structures forforming air gaps).

In some embodiments, the out-coupling optical elements 570, 580, 590,600, 610 are diffractive features that form a diffraction pattern, or“diffractive optical element” (also referred to herein as a “DOE”).Preferably, the DOE's have a sufficiently low diffraction efficiency sothat only a portion of the light of the beam is deflected away towardthe eye 210 with each intersection of the DOE, while the rest continuesto move through a waveguide via TIR. The light carrying the imageinformation is thus divided into a number of related exit beams thatexit the waveguide at a multiplicity of locations and the result is afairly uniform pattern of exit emission toward the eye 210 for thisparticular collimated beam bouncing around within a waveguide.

In some embodiments, one or more DOEs may be switchable between “on”states in which they actively diffract, and “off” states in which theydo not significantly diffract. For instance, a switchable DOE maycomprise a layer of polymer dispersed liquid crystal, in whichmicrodroplets comprise a diffraction pattern in a host medium, and therefractive index of the microdroplets may be switched to substantiallymatch the refractive index of the host material (in which case thepattern does not appreciably diffract incident light) or themicrodroplet may be switched to an index that does not match that of thehost medium (in which case the pattern actively diffracts incidentlight).

In some embodiments, a camera assembly 630 (e.g., a digital camera,including visible light and infrared light cameras) may be provided tocapture images of the eye 210 and/or tissue around the eye 210 to, e.g.,detect user inputs and/or to monitor the physiological state of theuser. As used herein, a camera may be any image capture device. In someembodiments, the camera assembly 630 may include an image capture deviceand a light source to project light (e.g., infrared light) to the eye,which may then be reflected by the eye and detected by the image capturedevice. In some embodiments, the camera assembly 630 may be attached tothe frame 80 (FIG. 2) and may be in electrical communication with theprocessing modules 140 and/or 150, which may process image informationfrom the camera assembly 630. In some embodiments, one camera assembly630 may be utilized for each eye, to separately monitor each eye.

With reference now to FIG. 7, an example of exit beams outputted by awaveguide is shown. One waveguide is illustrated, but it will beappreciated that other waveguides in the waveguide assembly 260 (FIG. 6)may function similarly, where the waveguide assembly 260 includesmultiple waveguides. Light 640 is injected into the waveguide 270 at theinput surface 460 of the waveguide 270 and propagates within thewaveguide 270 by TIR. At points where the light 640 impinges on the DOE570, a portion of the light exits the waveguide as exit beams 650. Theexit beams 650 are illustrated as substantially parallel but, asdiscussed herein, they may also be redirected to propagate to the eye210 at an angle (e.g., forming divergent exit beams), depending on thedepth plane associated with the waveguide 270. It will be appreciatedthat substantially parallel exit beams may be indicative of a waveguidewith out-coupling optical elements that out-couple light to form imagesthat appear to be set on a depth plane at a large distance (e.g.,optical infinity) from the eye 210. Other waveguides or other sets ofout-coupling optical elements may output an exit beam pattern that ismore divergent, which would require the eye 210 to accommodate to acloser distance to bring it into focus on the retina and would beinterpreted by the brain as light from a distance closer to the eye 210than optical infinity.

In some embodiments, a full color image may be formed at each depthplane by overlaying images in each of the component colors, e.g., threeor more component colors. FIG. 8 illustrates an example of a stackedwaveguide assembly in which each depth plane includes images formedusing multiple different component colors. The illustrated embodimentshows depth planes 240 a-240 f, although more or fewer depths are alsocontemplated. Each depth plane may have three or more component colorimages associated with it, including: a first image of a first color, G;a second image of a second color, R; and a third image of a third color,B. Different depth planes are indicated in the figure by differentnumbers for diopters (dpt) following the letters G, R, and B. Just asexamples, the numbers following each of these letters indicate diopters(1/m), or inverse distance of the depth plane from a viewer, and eachbox in the figures represents an individual component color image. Insome embodiments, to account for differences in the eye's focusing oflight of different wavelengths, the exact placement of the depth planesfor different component colors may vary. For example, differentcomponent color images for a given depth plane may be placed on depthplanes corresponding to different distances from the user. Such anarrangement may increase visual acuity and user comfort and/or maydecrease chromatic aberrations.

In some embodiments, light of each component color may be outputted by asingle dedicated waveguide and, consequently, each depth plane may havemultiple waveguides associated with it. In such embodiments, each box inthe figures including the letters G, R, or B may be understood torepresent an individual waveguide, and three waveguides may be providedper depth plane where three component color images are provided perdepth plane. While the waveguides associated with each depth plane areshown adjacent to one another in this drawing for ease of description,it will be appreciated that, in a physical device, the waveguides mayall be arranged in a stack with one waveguide per level. In some otherembodiments, multiple component colors may be outputted by the samewaveguide, such that, e.g., only a single waveguide may be provided perdepth plane.

With continued reference to FIG. 8, in some embodiments, G is the colorgreen, R is the color red, and B is the color blue. In some otherembodiments, other colors associated with other wavelengths of light,including magenta and cyan, may be used in addition to or may replaceone or more of red, green, or blue.

It will be appreciated that references to a given color of lightthroughout this disclosure will be understood to encompass light of oneor more wavelengths within a range of wavelengths of light that areperceived by a viewer as being of that given color. For example, redlight may include light of one or more wavelengths in the range of about620-780 nm, green light may include light of one or more wavelengths inthe range of about 492-577 nm, and blue light may include light of oneor more wavelengths in the range of about 435-493 nm.

In some embodiments, the light source 540 (FIG. 6) may be configured toemit light of one or more wavelengths outside the visual perceptionrange of the viewer, for example, infrared and/or ultravioletwavelengths. In addition, the in-coupling, out-coupling, and other lightredirecting structures of the waveguides of the display 250 may beconfigured to direct and emit this light out of the display towards theuser's eye 210, e.g., for imaging and/or user stimulation applications.

With reference now to FIG. 9A, in some embodiments, light impinging on awaveguide may need to be redirected to in-couple that light into thewaveguide. An in-coupling optical element may be used to redirect andin-couple the light into its corresponding waveguide. FIG. 9Aillustrates a cross-sectional side view of an example of a plurality orset 660 of stacked waveguides that each includes an in-coupling opticalelement. The waveguides may each be configured to output light of one ormore different wavelengths, or one or more different ranges ofwavelengths. It will be appreciated that the stack 660 may correspond tothe stack 260 (FIG. 6) and the illustrated waveguides of the stack 660may correspond to part of the plurality of waveguides 270, 280, 290,300, 310, except that light from one or more of the image injectiondevices 360, 370, 380, 390, 400 is injected into the waveguides from aposition that requires light to be redirected for in-coupling.

The illustrated set 660 of stacked waveguides includes waveguides 670,680, and 690. Each waveguide includes an associated in-coupling opticalelement (which may also be referred to as a light input area on thewaveguide), with, e.g., in-coupling optical element 700 disposed on amajor surface (e.g., an upper major surface) of waveguide 670,in-coupling optical element 710 disposed on a major surface (e.g., anupper major surface) of waveguide 680, and in-coupling optical element720 disposed on a major surface (e.g., an upper major surface) ofwaveguide 690. In some embodiments, one or more of the in-couplingoptical elements 700, 710, 720 may be disposed on the bottom majorsurface of the respective waveguide 670, 680, 690 (particularly wherethe one or more in-coupling optical elements are reflective, deflectingoptical elements). As illustrated, the in-coupling optical elements 700,710, 720 may be disposed on the upper major surface of their respectivewaveguide 670, 680, 690 (or the top of the next lower waveguide),particularly where those in-coupling optical elements are transmissive,deflecting optical elements. In some embodiments, the in-couplingoptical elements 700, 710, 720 may be disposed in the body of therespective waveguide 670, 680, 690. In some embodiments, as discussedherein, the in-coupling optical elements 700, 710, 720 are wavelengthselective, such that they selectively redirect one or more wavelengthsof light, while transmitting other wavelengths of light. Whileillustrated on one side or corner of their respective waveguide 670,680, 690, it will be appreciated that the in-coupling optical elements700, 710, 720 may be disposed in other areas of their respectivewaveguide 670, 680, 690 in some embodiments.

As illustrated, the in-coupling optical elements 700, 710, 720 may belaterally offset from one another. In some embodiments, each in-couplingoptical element may be offset such that it receives light without thatlight passing through another in-coupling optical element. For example,each in-coupling optical element 700, 710, 720 may be configured toreceive light from a different image injection device 360, 370, 380,390, and 400 as shown in FIG. 6, and may be separated (e.g., laterallyspaced apart) from other in-coupling optical elements 700, 710, 720 suchthat it substantially does not receive light from the other ones of thein-coupling optical elements 700, 710, 720.

Each waveguide also includes associated light distributing elements,with, e.g., light distributing elements 730 disposed on a major surface(e.g., a top major surface) of waveguide 670, light distributingelements 740 disposed on a major surface (e.g., a top major surface) ofwaveguide 680, and light distributing elements 750 disposed on a majorsurface (e.g., a top major surface) of waveguide 690. In some otherembodiments, the light distributing elements 730, 740, 750, may bedisposed on a bottom major surface of associated waveguides 670, 680,690, respectively. In some other embodiments, the light distributingelements 730, 740, 750, may be disposed on both top and bottom majorsurface of associated waveguides 670, 680, 690, respectively; or thelight distributing elements 730, 740, 750, may be disposed on differentones of the top and bottom major surfaces in different associatedwaveguides 670, 680, 690, respectively.

The waveguides 670, 680, 690 may be spaced apart and separated by, e.g.,gas, liquid, and/or solid layers of material. For example, asillustrated, layer 760 a may separate waveguides 670 and 680; and layer760 b may separate waveguides 680 and 690. In some embodiments, thelayers 760 a and 760 b are formed of low refractive index materials(that is, materials having a lower refractive index than the materialforming the immediately adjacent one of waveguides 670, 680, 690).Preferably, the refractive index of the material forming the layers 760a, 760 b is 0.05 or more, or 0.10 or less than the refractive index ofthe material forming the waveguides 670, 680, 690. Advantageously, thelower refractive index layers 760 a, 760 b may function as claddinglayers that facilitate total internal reflection (TIR) of light throughthe waveguides 670, 680, 690 (e.g., TIR between the top and bottom majorsurfaces of each waveguide). In some embodiments, the layers 760 a, 760b are formed of air. While not illustrated, it will be appreciated thatthe top and bottom of the illustrated set 660 of waveguides may includeimmediately neighboring cladding layers.

Preferably, for ease of manufacturing and other considerations, thematerial forming the waveguides 670, 680, 690 are similar or the same,and the material forming the layers 760 a, 760 b are similar or thesame. In some embodiments, the material forming the waveguides 670, 680,690 may be different between one or more waveguides, and/or the materialforming the layers 760 a, 760 b may be different, while still holding tothe various refractive index relationships noted above.

With continued reference to FIG. 9A, light rays 770, 780, 790 areincident on the set 660 of waveguides. It will be appreciated that thelight rays 770, 780, 790 may be injected into the waveguides 670, 680,690 by one or more image injection devices 360, 370, 380, 390, 400 (FIG.6).

In some embodiments, the light rays 770, 780, 790 have differentproperties, e.g., different wavelengths or different ranges ofwavelengths, which may correspond to different colors. The in-couplingoptical elements 700, 710, 720 each deflect the incident light such thatthe light propagates through a respective one of the waveguides 670,680, 690 by TIR. In some embodiments, the incoupling optical elements700, 710, 720 each selectively deflect one or more particularwavelengths of light, while transmitting other wavelengths to anunderlying waveguide and associated incoupling optical element.

For example, in-coupling optical element 700 may be configured todeflect ray 770, which has a first wavelength or range of wavelengths,while transmitting rays 780 and 790, which have different second andthird wavelengths or ranges of wavelengths, respectively. Thetransmitted ray 780 impinges on and is deflected by the in-couplingoptical element 710, which is configured to deflect light of a secondwavelength or range of wavelengths. The ray 790 is deflected by thein-coupling optical element 720, which is configured to selectivelydeflect light of third wavelength or range of wavelengths.

With continued reference to FIG. 9A, the deflected light rays 770, 780,790 are deflected so that they propagate through a correspondingwaveguide 670, 680, 690; that is, the in-coupling optical elements 700,710, 720 of each waveguide deflects light into that correspondingwaveguide 670, 680, 690 to in-couple light into that correspondingwaveguide. The light rays 770, 780, 790 are deflected at angles thatcause the light to propagate through the respective waveguide 670, 680,690 by TIR. The light rays 770, 780, 790 propagate through therespective waveguide 670, 680, 690 by TIR until impinging on thewaveguide's corresponding light distributing elements 730, 740, 750.

With reference now to FIG. 9B, a perspective view of an example of theplurality of stacked waveguides of FIG. 9A is illustrated. As notedabove, the in-coupled light rays 770, 780, 790, are deflected by thein-coupling optical elements 700, 710, 720, respectively, and thenpropagate by TIR within the waveguides 670, 680, 690, respectively. Thelight rays 770, 780, 790 then impinge on the light distributing elements730, 740, 750, respectively. The light distributing elements 730, 740,750 deflect the light rays 770, 780, 790 so that they propagate towardsthe out-coupling optical elements 800, 810, 820, respectively.

In some embodiments, the light distributing elements 730, 740, 750 areorthogonal pupil expanders (OPE's). In some embodiments, the OPE'sdeflect or distribute light to the out-coupling optical elements 800,810, 820 and, in some embodiments, may also increase the beam or spotsize of this light as it propagates to the out-coupling opticalelements. In some embodiments, the light distributing elements 730, 740,750 may be omitted and the in-coupling optical elements 700, 710, 720may be configured to deflect light directly to the out-coupling opticalelements 800, 810, 820. For example, with reference to FIG. 9A, thelight distributing elements 730, 740, 750 may be replaced without-coupling optical elements 800, 810, 820, respectively. In someembodiments, the out-coupling optical elements 800, 810, 820 are exitpupils (EP's) or exit pupil expanders (EPE's) that direct light in aviewer's eye 210 (FIG. 7). It will be appreciated that the OPE's may beconfigured to increase the dimensions of the eye box in at least oneaxis and the EPE's may be to increase the eye box in an axis crossing,e.g., orthogonal to, the axis of the OPEs. For example, each OPE may beconfigured to redirect a portion of the light striking the OPE to an EPEof the same waveguide, while allowing the remaining portion of the lightto continue to propagate down the waveguide. Upon impinging on the OPEagain, another portion of the remaining light is redirected to the EPE,and the remaining portion of that portion continues to propagate furtherdown the waveguide, and so on. Similarly, upon striking the EPE, aportion of the impinging light is directed out of the waveguide towardsthe user, and a remaining portion of that light continues to propagatethrough the waveguide until it strikes the EP again, at which timeanother portion of the impinging light is directed out of the waveguide,and so on. Consequently, a single beam of incoupled light may be“replicated” each time a portion of that light is redirected by an OPEor EPE, thereby forming a field of cloned beams of light, as shown inFIG. 6. In some embodiments, the OPE and/or EPE may be configured tomodify a size of the beams of light.

Accordingly, with reference to FIGS. 9A and 9B, in some embodiments, theset 660 of waveguides includes waveguides 670, 680, 690; in-couplingoptical elements 700, 710, 720; light distributing elements (e.g.,OPE's) 730, 740, 750; and out-coupling optical elements (e.g., EP's)800, 810, 820 for each component color. The waveguides 670, 680, 690 maybe stacked with an air gap/cladding layer between each one. Thein-coupling optical elements 700, 710, 720 redirect or deflect incidentlight (with different in-coupling optical elements receiving light ofdifferent wavelengths) into its waveguide. The light then propagates atan angle which will result in TIR within the respective waveguide 670,680, 690. In the example shown, light ray 770 (e.g., blue light) isdeflected by the first in-coupling optical element 700, and thencontinues to bounce down the waveguide, interacting with the lightdistributing element (e.g., OPE's) 730 and then the out-coupling opticalelement (e.g., EPs) 800, in a manner described earlier. The light rays780 and 790 (e.g., green and red light, respectively) will pass throughthe waveguide 670, with light ray 780 impinging on and being deflectedby in-coupling optical element 710. The light ray 780 then bounces downthe waveguide 680 via TIR, proceeding on to its light distributingelement (e.g., OPEs) 740 and then the out-coupling optical element(e.g., EP's) 810. Finally, light ray 790 (e.g., red light) passesthrough the waveguide 690 to impinge on the light in-coupling opticalelements 720 of the waveguide 690. The light in-coupling opticalelements 720 deflect the light ray 790 such that the light raypropagates to light distributing element (e.g., OPEs) 750 by TIR, andthen to the out-coupling optical element (e.g., EPs) 820 by TIR. Theout-coupling optical element 820 then finally out-couples the light ray790 to the viewer, who also receives the out-coupled light from theother waveguides 670, 680.

FIG. 9C illustrates a top-down plan view of an example of the pluralityof stacked waveguides of FIGS. 9A and 9B. As illustrated, the waveguides670, 680, 690, along with each waveguide's associated light distributingelement 730, 740, 750 and associated out-coupling optical element 800,810, 820, may be vertically aligned. However, as discussed herein, thein-coupling optical elements 700, 710, 720 are not vertically aligned;rather, the in-coupling optical elements are preferably non-overlapping(e.g., laterally spaced apart as seen in the top-down view). Asdiscussed further herein, this nonoverlapping spatial arrangementfacilitates the injection of light from different resources intodifferent waveguides on a one-to-one basis, thereby allowing a specificlight source to be uniquely coupled to a specific waveguide. In someembodiments, arrangements including nonoverlapping spatially-separatedin-coupling optical elements may be referred to as a shifted pupilsystem, and the in-coupling optical elements within these arrangementsmay correspond to sub pupils.

Reference will now be made to FIGS. 10A and 10B. Some embodiments ofaugmented reality devices, such as those described above, may beconfigured to adjust the wavefront of light (including light for imageinformation projected from the augmented reality system as well asincoming light from objects in the surrounding real world) by tuningfocal lengths of variable focus lens elements included in the augmentedreality system. As discussed above, the augmented reality system maycomprise a display device that may include a plurality of stackedwaveguides (e.g., corresponding to the plurality or set 660 of stackedwaveguides of FIGS. 9A and 9B, or corresponding to the stacked waveguideassembly 260 of FIG. 6) that project light towards the eyes of a user ora viewer (e.g., the viewer or user 90 of FIG. 2). In some otherembodiments, the display device may include only a single waveguide.Consequently, while plural waveguides are referenced in various parts ofthe disclosure herein, it will be appreciated that the plural waveguidesmay be replaced by a singular waveguide.

As discussed herein, the projected light from the waveguides may be usedto provide virtual, augmented reality image information to the viewer.The light may be projected such that the user perceives the light tooriginate from one or more different depths, or distances from theviewer. The display device may be optically transmissive, such that theuser can see real-world objects in the surrounding environment throughthe display device. In some embodiments, the waveguides may beconfigured to have fixed optical power. To provide the appearance thatthe projected light is originating from different depths, the waveguidesmay be configured to output divergent beams of light, with differentamounts of divergence corresponding to different depth planes.

It will be appreciated that the fixed optical power of the waveguidesassumes that the viewer's eyes have a suitable accommodative range tofocus the light outputted by the waveguides. As discussed above,however, some viewers may require corrective lens to see clearly and, asa result, the image information outputted from a waveguide may not beclearly seen by such viewers. In some embodiments, a first variablefocus lens element may be provided between the waveguide and theviewer's eye to provide an appropriate adjustment to the wavefront ofthe light outputted by the waveguide, to allow this light to becorrectly focused by the viewer's eye. This first lens element, however,is also in the path of light propagating from the surroundingenvironment to the viewer's eye. As a result, the first lens element maymodify the wavefront of the light from the surrounding environment and,thereby cause aberrations in the viewer's view of the world. To correctsuch aberrations, a second variable focus lens element may be disposedon the opposite side of the plurality of stacked waveguides from thefirst variable focus lens element; that is, the second variable focuslens element may be between the plurality of stacked waveguides and thesurrounding real world to adjust the wavefront of light from real-worldobjects in the surrounding environment. The second variable focus lenselement may be configured to compensate for aberrations caused by thefirst variable focus lens element. In some embodiments, the secondvariable focus lens may also be configured to compensate for aberrationscaused by the waveguides.

In some embodiments, the focus of the second variable focus lens elementmay be inverse or opposite the focus of the first variable focus lenselement. For example, if the first variable focus lens element has apositive optical power, then the second variable focus lens element mayhave a negative optical power, which may be of similar magnitude. Insome other embodiments, to compensate for both the optical power of thefirst variable focus lens element and the optical power of theintervening waveguides, the optical power of the second lens elementsmay be opposite to and of similar magnitude as the aggregate opticalpower of the first lens element and the waveguides.

In some other embodiments, the waveguides may not have optical power(e.g., the waveguides may be configured to output collimated light), andthe first variable focus lens elements may be configured to modify thewavefront of light emitted from the waveguides to provide theappropriate amount of divergence for image information to be interpretedby the viewer as being on a particular depth plane. It will beappreciated that the appropriate amount of divergence may vary fordifferent viewers since optical power for placing image information on aparticular depth plane will be adjusted by a particular differential toaccount for a viewer's optical prescription for that depth plane. Insuch embodiments, the waveguide stack between the first and secondvariable focus lens elements may simply be formed by a single waveguide.

It will be appreciated that the first and second variable focus lenselements may be provided for one of the viewer's eyes, and that thirdand fourth variable focus lens elements that are similar to the firstand second variable focus lens elements, respectively, may be providedfor the other of the viewer's eyes.

FIGS. 10A and 10B show schematic illustrations of examples of displaysystems (e.g., augmented reality display systems) having variable focuslens elements and a waveguide stack. It will be appreciated that thedisplay system 2010 may correspond to the display system 250 (FIG. 6).The example display system 2010 of FIG. 10A shows a waveguide stack witha single waveguide, while the example of FIG. 10B shows a waveguidestack with a plurality of waveguides. In both FIGS. 10A and 10B, a firstvariable focus lens element 2007 a and a second variable focus lenselement 2007 b are disposed on either side of a waveguide stack 2005(FIG. 10A), and a third variable focus lens element 2008 a and a fourthvariable focus lens element 2008 b are disposed on either side of awaveguide stack 2006 (FIG. 10B).

The various illustrated waveguides 2005 a, 2005 b, 2006 a, 2006 b ofFIGS. 10A and 10B may have characteristics and/or features similar toindividual ones of waveguides 270, 280, 290, 300, 310 of FIG. 6 and/orwaveguides 670, 680, and 690 of FIGS. 9A and 9B. The waveguide stacks2005, 2006 may have characteristics and/or features similar to theplurality or set 660 of stacked waveguides of FIGS. 9A and 9B or to thestacked waveguide assembly 260 of FIG. 6. In some embodiments, thewaveguides 2005 a, 2005 b, 2006 a, 2006 b may include optical elements,such as diffractive optical elements, that provide the waveguides withoptical power, e.g., a fixed optical power. For example, one or more ofthese waveguides may have an optical power in the range between 0Diopter and about 5.0 Diopters, between about 0.5 Diopters and about 4.5Diopters, between about 1.0 Diopters and about 4.0 Diopters, betweenabout 1.5 Diopters and about 3.5 Diopters, between about 2.0 Dioptersand about 3.0 Diopters, or any value in these ranges or sub-ranges. Asanother example, in a particular embodiment, each of the waveguides mayhave an optical power of 1.5 Diopters.

As discussed above, light providing image information (e.g., virtualcontent) from an optical source 2003 or 2004 may be injected into thewaveguide 2005 a or 2006 a, respectively, such that the light propagatesthrough each of those waveguides by total internal reflection. Thepropagating light may be projected out of the waveguide 2005 a (orwaveguide 2005 b) by out-coupling elements (e.g., corresponding toout-coupling elements 800, 810, 820 of FIGS. 9A and 9B) towards theuser's eye 2001. In some embodiments, the optical sources 2003, 2004 maybe fiber scanning devices (FSD) that utilize a moving fiber to create a2D image pattern, as disclosed herein. The FSD may create the 2D imagepattern by projecting light in a variety of patterns, such as, forexample, raster scan, spiral scan, Lissajous, etc. In some otherembodiments, the optical source 2003 a (and/or 2003b) may be an imageprojection system, e.g. in which a full image is projected onto awaveguide, as also disclosed herein. It will be appreciated that lightfrom the optical source 2003 a (and/or 2003b) may be injected into thewaveguide stack 2005 through edges of the waveguides or through a majorsurface of the waveguide. Where the waveguide stack includes a pluralityof waveguides, the optical source 2003 and/or 2004 may be configured toinject light into multiple ones of these waveguides, or additionaloptical sources, e.g., one optical source for each waveguide, may beprovided.

As illustrated in FIGS. 10A and 10B, the first variable focus lenselement 2007 a may be disposed between the waveguide stack 2005 and theuser's eye 2001, and the second variable focus lens element 2007 b maybe disposed between the waveguide stack 2005 and the real worldsurrounding the user. It will be appreciated that the eye 2001 maycorrespond to the viewer's eye 210 of FIG. 6. Similarly, the thirdvariable focus lens element 2008 a may be disposed between the waveguidestack 2006 and the user's eye 2002 and the second variable focus lenselement 2008 b may be disposed between the waveguide stack 2006 and thereal world surrounding the user.

In some embodiments, the first and the second variable focus lenselements 2007 a and 2007 b, and third and fourth variable focus lenselements 2008 a and 2008 b, may be adaptable optical elements. Theadaptable optical elements may be dynamically altered, for example, byapplying an electrical signal thereto, to change the shape of awavefront that is incident thereon. In some embodiments, the adaptableoptical elements may comprise a transmissive optical element such as adynamic lens (e.g., a liquid crystal lens, an electro-active lens, aconventional refractive lens with moving elements, amechanical-deformation-based lens, an electrowetting lens, anelastomeric lens, or a plurality of fluids with different refractiveindices). By altering the adaptable optics' shape, refractive index, orother characteristics, the wavefront incident thereon may be changed,for example, to alter the focus of the light by the viewer's eyes, asdescribed herein.

In some embodiments, the variable focus lens elements 2007 a, 2007 b,2008 a, 2008 b may comprise a layer of liquid crystal sandwiched betweentwo substrates. The substrates may comprise an optically transmissivematerial such as, for example, glass, plastic, acrylic, etc. In someembodiments, the substrates may be flat. In some embodiments, thesubstrates may have curved regions such that portions of the substratesmay have fixed optical power.

In some embodiments, the optical power of the variable focus lenselements 2007 a, 2007 b, 2008 a, 2008 b may be varied by adjusting anelectrical signal (e.g., current and/or voltage) applied to the liquidcrystal layer via, e.g., one or more thin film transistors (TFTs) and/orelectrodes integrated with the liquid crystal layer and/or thesubstrates. It will be appreciated that the orientations of liquidcrystal species in the liquid crystal layer determines the refractiveindex of the layer. The applied electrical signal sets the orientationof the liquid crystal species, thereby allowing the refractive index ofthe liquid crystal layer to be varied as desired by altering the appliedelectrical signal. In some embodiments, the optical power of thevariable focus lens elements 2007 a, 2007 b, 2008 a, 2008 b may bevaried between about ±5.0 Diopters (e.g., between about −4.0 Dioptersand +4.0 Diopters; between about −3.5 Diopters and about +3.5 Diopters,between about −3.0 Diopters and about +3.0 Diopters, between about −2.0Diopters and about +2.0 Diopters, between about −1.5 Diopters and about+1.5 Diopters, including values in any of these ranges or sub-ranges).

Advantageously, the variable focus lens elements 2007 a, 2007 b, 2008 a,2008 b may have a wide aperture that is substantially matched to theaperture of the waveguides of their respective associated waveguidestacks 2005, 2006. In some embodiments, the apertures of the variablefocus lens elements 2007 a, 2007 b, 2008 a, 2008 b may be substantiallyequal (e.g., within about ±20%, about ±15%, or about ±10%) to thesurface areas of the waveguides of the waveguide stacks 2005, 2006.Consequently, the areas over which the variable focus lens elements 2007a, 2007 b, 2008 a, 2008 b and the waveguide stacks 2005, 2206 transmitlight to an associated eye 2001, 2002 may be substantially equal.

With continued reference to FIGS. 10A and 10B, the first and thirdvariable focus lens elements 2007 a, 2008 a may each have its opticalpower varied to adjust the wavefront of light projected from a waveguideof the waveguide stacks 2005, 2006, respectively, to properly focus thatlight onto the retina of the eyes 2001, 2002, respectively. As notedherein, the first and third variable focus lens elements 2007 a, 2008 amay cause aberrations in the wavefront of incoming light from an object2009 in the surrounding environment, thereby diminishing the opticalimage quality of real-world objects 2009 viewed through the firstvariable focus lens element 2007 a. The second and fourth variable focuslens elements 2007 b, 2008 b may advantageously compensate for theaberrations introduced by the first and third variable focus lenselements 2007 a, 2008 a, respectively, and any waveguides when viewingthe object 2009. In some embodiments, the second and fourth variablefocus lens elements 2007 b, 2008 b may be configured to provide anoptical power opposite to the optical power provided by the first andthird variable focus lens elements 2007 a, 2008 a, respectively, and theassociated waveguide stack 2005, 2006. In some embodiments, themagnitude of the opposite optical power is such that the net opticalpower of the display system 2010, for each eye 2001, 2002, is equal toan optical prescription for the eye at the depth plane that the eye isverging towards. The optical power provided by the first and the secondvariable focus lens elements 2007 a and 2007 b may be varied andcontrolled by an electronic hardware control system 2011. In someembodiments, the electronic hardware control system 2011 may correspondto the local processing and data module 140 and/or the remote processingmodule 150 of FIG. 2.

In some embodiments, the augmented reality display system 2010 may beconfigured to determine vergence of the user's eyes. The optical powerof the first and the second variable focus lens elements 2007 a, 2007 bmay be set based upon the vergence point of the eyes 2001, 2002. Theoptical power of the third and the fourth variable focus lens elements2008 a, 2008 b may also be set based upon this vergence point. It willbe appreciated that the vergence point is the point in space at whichthe lines of sight of the eyes 2001, 2002 converge and may correspond tothe physiologic accommodation target of those eyes. In some embodiments,the distance that the point is away from the eyes 2001, 2002 may becalculated based, e.g., on the known quantities of the separationbetween the eyes 2001, 2002 and the angles made out by the each eye.Once that distance is calculated, an appropriate correction for theviewer for that distance may be determined. For example, the displaysystem 2010 may be programmed with one or more optical prescriptions. Insome embodiments, the optical prescriptions may be stored in the localprocessing and data module 140 and/or the remote data repository 160.The distance between the eyes 2001, 2002 and the vergence point may bematched with the appropriate correction for that distance, and thevariable focus lens elements 2007 a, 2007 b, 2008 a, 2008 b may beadjusted to provide the correction. In some embodiments, the eyes 2001,2002 may have different prescribed corrections and, as a result, thepairs of variable focus lens elements 2007 a, 2007 b, and 2008 a, 2008b, may provide different optical power.

Advantageously, the variable focus lens elements 2007 a, 2007 b, 2008 a,2008 b provide for a large number of possible corrections since theiroptical power can be adjusted as desired by, e.g., the application ofdifferent voltages. In some embodiments, the total number of correctionsper eye maybe 1, 2, 3, or 4 more. In some embodiments, the total numberof corrections per eye may be equal to the number of depth planes thatthe display system 2010 is configured to display image information on.It will be appreciated that these corrections may correspond to opticalprescriptions, which may be determined for objects at various distancesfrom the eyes 2001, 2002. For example, four prescriptions may beobtained by determining corrections for refractive errors at fourprogressively farther distances (e.g., close, close intermediate, farintermediate, and far distances) from the eyes 2001, 2002. In someembodiments, the number of possible corrections for viewing imagecontent outputted by the waveguide stack 2005 may be different from thenumber of possible corrections when viewing objects 2009 in thesurrounding environment.

With continued reference to FIGS. 10A and 10B, in some embodiments, thefocus, or optical power, of the variable focus lens elements 2007 a,2007 b, 2008 a, 2008 b may each be set based upon the determinedvergence of the user's eyes 2001, 2004. For example, the optical powerof the first and the second variable focus lens elements 2007 a and 2007b may be varied based on the vergence of the user's eyes 2001 withoutspecific reference to the optical power of the other lens element.

In some embodiments, one of the first and the second variable focus lenselements 2007 a, 2007 b, or one of the third and the fourth variablefocus elements 2008 a, 2008 b, may be designated as a master and theother of the first and the second variable focus lens elements 2007 a,2007 b, or the third and the fourth variable focus elements 2008 a, 2008b, may be designated as a slave. The variable focus lens elementdesignated as the slave may be configured to follow the master variablefocus lens element. In some other embodiments, the second and the fourthvariable focus lens elements 2007 b, 2008 b may be slaved to the firstand third variable focus lens elements 2007 a, 2008 a, and the focus ofthe first and third variable focus lens elements 2007 a, 2008 a may beset based upon the determined vergence point of the user's eyes 2001,2002. For example, if the waveguide 2005 a (and/or waveguide 2005 b) hasan optical power of about 1.5 Diopters and the user is verging at 2.0Diopters, the first variable focus lens element 2007 a may have anoptical power of +0.5 Diopters and the second variable focus lenselement 2007 b may have an optical power −0.5 Diopters.

The optical powers of the variable focus lens elements 2007 a, 2007 b,2008 a, 2008 b may be varied in real time, and may preferably be changedat a rate equal to or greater than the rate at which the human eyechanges accommodation states. Preferably, the first and second variablefocus lens elements can change their optical power before the human eyechanges accommodation states, such that the user does not experience adelay in receiving the appropriate correction for a given vergencepoint. In some embodiments, the first and second variable focus lenselements can change in optical power in less than about 300 ms, lessthan about 275 ms, or less than about 250 ms. The electronic hardwarecontrol system 2011 may drive the variable focus lens elements 2007 a,2007 b, 2008 a, 2008 b such that the optical powers of the variablefocus lens elements 2007 a, 2007 b, 2008 a, 2008 b may be variedsimultaneously.

Various embodiments of the augmented reality display systems describedherein may include an eye tracking system comprising one or more eyetracking cameras or imaging systems to track one or more eyes of theuser to determine/measure the vergence of the user's eyes. An exampleembodiment of an augmented reality system 2010 including an eye trackingsystem 22 is illustrated in FIG. 11. The eye tracking system 22 mayinclude cameras 24 (e.g., infrared cameras) paired with light sources 26(e.g., infrared light sources) directed at and configured to monitor andtrack the eyes 2001, 2002 of the user. These cameras 24 and lightsources 26 may be operatively coupled to the local processing module140. Such cameras 24 may monitor one or more of the orientations, pupilsizes, and the corresponding direction of the line of sight of therespective eyes. As described herein, the cameras 24 may be configuredto determine the vergence point of the eyes 2001, 2002.

With continued reference to FIG. 11, the cameras 24 and light sources 26may be mounted on the frame 80, which may also hold the waveguide stacks2005, 2006. In some embodiments, the cameras 24 may communicate with thelocal processing and data module 140 through communication links 170,180.

In some embodiments, in addition to determining the vergence of the eyes2001, 2002, the cameras 24 may be utilized to track the eyes to provideuser input. For example, the eye-tracking system 22 may be utilized toselect items on virtual menus, and/or provide other input to the displaysystem 2010.

With reference now to FIG. 12A, a flowchart 2200 is provided depictingan example method of varying the optical power of variable focus lenselements based on the determined vergence of a user. At block 2205, thevergence point of the user's eyes may be determined or measured. Such adetermination may be made using, e.g., the eye-tracking systemsdescribed herein. Based on this determination, the distance and/or depthplane at which the user's eyes are directed may be estimated. Theoptical power of a pair of variable lens elements may be varied inaccordance with the determined vergence to improve the image quality ofthe virtual objects and/or real-world objects viewed by the user. Atblock 2215, the optical power of a variable focus lens element (e.g.,one of the variable focus lens elements 2007 a, 2007 b, 2008 a, 2008 b)is varied to adjust a wavefront of light projected from a waveguide,such as a waveguide of the waveguide stacks 2005, 2006 (FIGS. 10A and10B). At block 2220, the optical power of another variable focus lenselement (e.g., a different one of the variable focus lens elements 2007a, 2007 b, 2008 a, 2008 b) is varied to adjust a wavefront of incomingambient light from an object in the surrounding environment. It will beappreciated that blocks 2215, 2220 may be performed sequentially (e.g.,with 2215 performed before 2220, or vice versa), or these blocks 2215,2220 maybe performed concurrently. In some embodiments, blocks 2205,2215, 2220 may be performed continuously by the display system 2010 toautomatically and continuously adjust the optical powers of the variablefocus lens elements to provide a comfortable viewing experience for theuser.

It will be appreciated that each of the processes, methods, andalgorithms described herein and/or depicted in the figures may beembodied in, and fully or partially automated by, code modules executedby one or more physical computing systems, hardware computer processors,application-specific circuitry, and/or electronic hardware configured toexecute specific and particular computer instructions. For example,computing systems may include general purpose computers (e.g., servers)programmed with specific computer instructions or special purposecomputers, special purpose circuitry, and so forth. A code module may becompiled and linked into an executable program, installed in a dynamiclink library, or may be written in an interpreted programming language.In some embodiments, particular operations and methods may be performedby circuitry that is specific to a given function.

Further, certain embodiments of the functionality of the presentdisclosure are sufficiently mathematically, computationally, ortechnically complex that application-specific hardware or one or morephysical computing devices (utilizing appropriate specialized executableinstructions) may be necessary to perform the functionality, forexample, due to the volume or complexity of the calculations involved orto provide results substantially in real-time. For example, a video mayinclude many frames, with each frame having millions of pixels, andspecifically programmed computer hardware is necessary to process thevideo data to provide a desired image processing task or application ina commercially reasonable amount of time.

Code modules or any type of data may be stored on any type ofnon-transitory computer-readable medium, such as physical computerstorage including hard drives, solid state memory, random access memory(RAM), read only memory (ROM), optical disc, volatile or non-volatilestorage, combinations of the same and/or the like. In some embodiments,the non-transitory computer-readable medium may be part of one or moreof the local processing and data module (140), the remote processingmodule (150), and remote data repository (160). The methods and modules(or data) may also be transmitted as generated data signals (e.g., aspart of a carrier wave or other analog or digital propagated signal) ona variety of computer-readable transmission mediums, includingwireless-based and wired/cable-based mediums, and may take a variety offorms (e.g., as part of a single or multiplexed analog signal, or asmultiple discrete digital packets or frames). The results of thedisclosed processes or process steps may be stored, persistently orotherwise, in any type of non-transitory, tangible computer storage ormay be communicated via a computer-readable transmission medium.

Any processes, blocks, states, steps, or functionalities in flowdiagrams described herein and/or depicted in the attached figures shouldbe understood as potentially representing code modules, segments, orportions of code which include one or more executable instructions forimplementing specific functions (e.g., logical or arithmetical) or stepsin the process. The various processes, blocks, states, steps, orfunctionalities may be combined, rearranged, added to, deleted from,modified, or otherwise changed from the illustrative examples providedherein. In some embodiments, additional or different computing systemsor code modules may perform some or all of the functionalities describedherein. The methods and processes described herein are also not limitedto any particular sequence, and the blocks, steps, or states relatingthereto may be performed in other sequences that are appropriate, forexample, in serial, in parallel, or in some other manner. Tasks orevents may be added to or removed from the disclosed exampleembodiments. Moreover, the separation of various system components inthe embodiments described herein is for illustrative purposes and shouldnot be understood as requiring such separation in all embodiments. Itshould be understood that the described program components, methods, andsystems may generally be integrated together in a single computerproduct or packaged into multiple computer products.

In the foregoing specification, the invention has been described withreference to specific embodiments thereof. It will, however, be evidentthat various modifications and changes may be made thereto withoutdeparting from the broader spirit and scope of the invention. Thespecification and drawings are, accordingly, to be regarded in anillustrative rather than restrictive sense.

Indeed, it will be appreciated that the systems and methods of thedisclosure each have several innovative aspects, no single one of whichis solely responsible or required for the desirable attributes disclosedherein. The various features and processes described above may be usedindependently of one another, or may be combined in various ways. Allpossible combinations and subcombinations are intended to fall withinthe scope of this disclosure.

Certain features that are described in this specification in the contextof separate embodiments also may be implemented in combination in asingle embodiment. Conversely, various features that are described inthe context of a single embodiment also may be implemented in multipleembodiments separately or in any suitable subcombination. Moreover,although features may be described above as acting in certaincombinations and even initially claimed as such, one or more featuresfrom a claimed combination may in some cases be excised from thecombination, and the claimed combination may be directed to asubcombination or variation of a subcombination. No single feature orgroup of features is necessary or indispensable to each and everyembodiment.

It will be appreciated that conditional language used herein, such as,among others, “can,” “could,” “might,” “may,” “e.g.,” and the like,unless specifically stated otherwise, or otherwise understood within thecontext as used, is generally intended to convey that certainembodiments include, while other embodiments do not include, certainfeatures, elements and/or steps. Thus, such conditional language is notgenerally intended to imply that features, elements and/or steps are inany way required for one or more embodiments or that one or moreembodiments necessarily include logic for deciding, with or withoutauthor input or prompting, whether these features, elements and/or stepsare included or are to be performed in any particular embodiment. Theterms “comprising,” “including,” “having,” and the like are synonymousand are used inclusively, in an open-ended fashion, and do not excludeadditional elements, features, acts, operations, and so forth. Also, theterm “or” is used in its inclusive sense (and not in its exclusivesense) so that when used, for example, to connect a list of elements,the term “or” means one, some, or all of the elements in the list. Inaddition, the articles “a,” “an,” and “the” as used in this applicationand the appended claims are to be construed to mean “one or more” or “atleast one” unless specified otherwise. Similarly, while operations maybe depicted in the drawings in a particular order, it is to berecognized that such operations need not be performed in the particularorder shown or in sequential order, or that all illustrated operationsbe performed, to achieve desirable results. Further, the drawings mayschematically depict one more example processes in the form of aflowchart. However, other operations that are not depicted may beincorporated in the example methods and processes that are schematicallyillustrated. For example, one or more additional operations may beperformed before, after, simultaneously, or between any of theillustrated operations. Additionally, the operations may be rearrangedor reordered in other embodiments. In certain circumstances,multitasking and parallel processing may be advantageous. Moreover, theseparation of various system components in the embodiments describedabove should not be understood as requiring such separation in allembodiments, and it should be understood that the described programcomponents and systems may generally be integrated together in a singlesoftware product or packaged into multiple software products.Additionally, other embodiments are within the scope of the followingclaims. In some cases, the actions recited in the claims may beperformed in a different order and still achieve desirable results.

Accordingly, the claims are not intended to be limited to theembodiments shown herein, but are to be accorded the widest scopeconsistent with this disclosure, the principles and the novel featuresdisclosed herein.

What is claimed is:
 1. A display system comprising: a head-mountabledisplay configured to display a virtual object on one or more depthplanes, the display comprising: a first variable focus lens element; asecond variable focus lens element; one or more waveguides between thefirst variable focus lens element and the second variable focus lenselement, wherein the one or more waveguides are configured to: outputlight for forming the virtual object, and transmit light from asurrounding environment through the one or more waveguides; and an eyetracking system, wherein the display system is configured to: determineeye parameters indicative of a vergence of a viewer's eyes; and causethe second variable focus lens element to modify a wavefront divergenceof the light outputted from the one or more waveguides to display thevirtual object on a depth plane, wherein an amount of the modificationof the wavefront divergence is based on the eye parameters indicative ofthe vergence and on an amount to correct a refractive error of a firsteye of the viewer.
 2. The display system of claim 1, wherein the systemis further configured to project another virtual object to the viewervia the one or more waveguides, wherein the another virtual object isdisposed on a different depth plane than the virtual object, and whereinthe amount of modification of wavefront divergence is based on the depthplane of the virtual object when the determined depth of the vergence ofthe viewer's eyes corresponds to the depth plane of the virtual objectand the amount of modification of the wavefront divergence is based onthe depth plane of the another virtual object when the determined depthof the vergence of the viewer's eyes corresponds to the depth plane ofthe another virtual object, wherein the amounts of modification for thevirtual object and for the other virtual object are different.
 3. Thedisplay system of claim 1, wherein the display system is configured tocause the first variable focus lens element to modify a wavefrontdivergence of incoming light from the surrounding environment, whereinan amount of the modification of the wavefront divergence modified bythe first variable focus lens element is based on the determined eyeparameters indicative of the vergence of the viewer's eyes and on anamount to correct the refractive error of the viewer's first eye.
 4. Thedisplay system of claim 1 wherein the display system is configured toadjust the amount of corrected refractive error of the first variablefocus lens element in response to the amount of corrected refractiveerror of the second variable focus lens element.
 5. The display systemof claim 1, wherein the one or more waveguides are configured to outputlight with a divergent wavefront to the viewer to display the virtualobject.
 6. The display system of claim 1, wherein the one or morewaveguides comprises a plurality of waveguides each having a fixedoptical power.
 7. The display system of claim 6, wherein at least someof the waveguides have different optical powers than others of thewaveguides.
 8. The display system of claim 1, further comprising: athird variable focus element; a fourth variable focus element; and oneor more second waveguides between the third variable focus lens elementand the fourth variable focus lens element, wherein the one or moresecond waveguides are configured to: output light for forming thevirtual object in a second eye of the viewer, and transmit light fromthe surrounding environment through the one or more second waveguides.9. The display system of claim 8, wherein the display system isconfigured to cause the fourth variable focus lens element to modify awavefront divergence of the outputted light for forming the virtualobject on a depth plane, wherein an amount of the modification of thewavefront divergence is based on the eye parameters and on an amount tocorrect a refractive error of the second eye of the viewer.
 10. Thedisplay system of claim 9, wherein the display system is configured tocause the third variable focus lens element to modify a wavefrontdivergence of incoming light from the surrounding environment, whereinan amount of the modification of the wavefront divergence of incominglight is based on the determined eye parameters indicative of thevergence of the viewer's eyes and on an amount to correct the refractiveerror of the viewer's second eye.
 11. The display system of claim 1,wherein the amount to correct refractive error is adjusted in accordancewith a prescription for correcting the vision of the viewer's first eyeat two or more distances.
 12. The display system of claim 1, wherein thedisplay system has three or more preset prescriptions for refractiveerrors for each of the first and second variable focus lens elements.13. The display system of claim 1, wherein a number of availablerefractive error prescriptions is equal to at least a total number ofdepth planes for the display.
 14. The display system of claim 1, whereinone or both of the first and second variable focus lens elementscomprises a layer of liquid crystal sandwiched between two substrates.15. The display system of claim 14, further comprising an electronichardware control system configured to vary the refractive index of thefirst and/or second variable focus lens element by application of anelectrical current or voltage.
 16. A method for displaying images on ahead-mountable display, the method comprising: providing the displaymounted on a head of a viewer, the display configured to display avirtual object on one or more depth planes and comprising: a firstvariable focus lens element facing a surrounding environment; a secondvariable focus lens element facing the viewer; and one or morewaveguides between the first variable focus lens element and the secondvariable focus lens element, wherein the one or more waveguides areconfigured to: output light for forming the virtual object, and transmitlight from a surrounding environment to the viewer; determining eyeparameters indicative of a vergence of the viewer's eyes; and correctinga refractive error of a first eye of the viewer by: varying opticalpower of the second variable focus lens element, wherein the secondvariable focus lens element modifies a wavefront divergence of theoutputted light for forming the virtual object on a depth plane, whereinan amount of the modification of the wavefront divergence is based onthe eye parameters indicative of the vergence of the viewer's eyes andon an amount to correct the refractive error of the first eye; andvarying optical power of the first variable focus lens element, whereinthe optical power of the first variable focus lens element modifies awavefront divergence of incoming light from the surrounding environment,wherein an amount of the modification of the wavefront divergence of theincoming light is based on the eye parameters indicative of the vergenceof the viewer's eyes and on an amount to correct the refractive error ofthe first eye.
 17. The method of claim 16, further comprising:providing: a third variable focus element; a fourth variable focuselement; and one or more second waveguides between the third variablefocus lens element and the fourth variable focus lens element; andcorrecting a refractive error of a second eye of the viewer by: varyingan optical power of the fourth variable focus lens element, wherein thefourth variable focus lens element modifies a wavefront divergence ofthe outputted light for forming the virtual object on the depth plane,wherein an amount of the modification of the wavefront divergence isbased on the eye parameters indicative of the vergence of the viewer'seyes and on an amount to correct the refractive error of the viewer'ssecond eye; and varying an optical power of the third variable focuslens element, wherein the third variable focus lens element modifies awavefront divergence of the incoming light from the surroundingenvironment, wherein an amount of the modification of the wavefrontdivergence is based on the eye parameters indicative of the vergence ofthe viewer's eyes and on an amount to correct the refractive error ofthe viewer's second eye.
 18. The method of claim 17, wherein determiningeye parameters indicative of a vergence of the viewer's eyes comprisestracking the first and second eyes of the viewer using one or morecameras.
 19. The method of claim 16, wherein the optical power of thefirst variable focus lens element is varied simultaneously with theoptical power of the second variable focus lens element.
 20. The methodof claim 16, wherein the one or more waveguides each comprisesdiffractive optical elements configured to output divergent light fromthe waveguides.